L'Affaire des poisons (1955)

Madame de Montespan, the Maîtresse-en-titre of Louis XIV, has been in disgrace since the King set eyes on a younger beauty, Marie-Angélique Scorailles. Having had enough of the situation, the rejected mistress decides to visit La Voisin, a woman known as a fortune teller, a doctor, a midwife and who is also said to arrange black masses and sell poisons. Some time later Marie-Angélique, now Duchess of Fontanges, dies mysteriously aged only twenty...